MathematicsMedium202×since 2002Q5763Let a→\overrightarrow aa and b→\overrightarrow bb be two unit vectors. If the vectors c→=a^+2b^\,\overrightarrow c = \widehat a + 2\widehat bc=a+2b and d→=5a^−4b^\overrightarrow d = 5\widehat a - 4\widehat bd=5a−4b are perpendicular to each other, then the angle between a→\overrightarrow aa and b→\overrightarrow bb is :Aπ6{\pi \over 6}6πBπ2{\pi \over 2}2πCπ3{\pi \over 3}3πDπ4{\pi \over 4}4πCheck answerSkip